Method of brazing corrosion resistant nickel-based thin-walled tubing to stainless steel base members

Abstract

A method of brazing corrosion resistant, nickel-based, thin-walled tubing which includes substantial proportions of nickel, chromium and molybdenum to a stainless steel base member using a filler metal, principally comprising gold as a major constituent and nickel as a minor constituent, in a vacuum furnace without introducing stress corrosion cracks in the brazed tubing and also avoiding carbon precipitation. The brazing is conducted at a temperature of at least about 1900° F. (1038° C.) for a sufficient period of time to allow any carbide precipitation formed during the heating to redissolve and also to permit full, uniform flow of the filler metal. The heated members are rapidly quenched in an inert atmosphere to a temperature at least sufficiently low to avoid carbon precipitation in the tubing.

I claim: 
     
       1. The method of brazing corrosion resistant, nickel-based, thin-walled tubing which includes substantial proportions of nickel, chromium and molybdenum with an iron content limited to a maximum of 7 percent by weight to a stainless steel base member without introducing stress corrosion cracks in the tubing and also avoiding carbon precipitation in the brazed corrosion resistant tubing, which method comprises: retaining said tubing and said base member to be brazed in adjacent positions desired for the brazed product and positioning a filler metal principally comprising gold as a major constituent and nickel as a minor constituent proximate the adjacent portions of said tubing and said base member;   evenly heating said tubing and said base member and said filler metal under vacuum conditions to a temperature of at least about 1900° F. for a sufficient period of time to avoid excessive reaction between said filler metal and said parts being brazed and to allow any carbide precipitate formed during heating to redissolve and to permit full uniform flow of said filler metal between said tubing and said base member; and   rapidly quenching said retained and heated members in a gaseous atmosphere which is non-reactive with respect to said retained and heated members to a temperature at least sufficiently low to avoid carbide precipitation in said tubing.   
     
     
       2. The method as specified in claim 1, wherein said filler metal also includes a predetermined small proportion of palladium, and said even heating temperature is sufficient to cause said filler metal to evenly flow. 
     
     
       3. The method as specified in claim 1, wherein said tubing has a wall thickness of less than about 12 mils. 
     
     
       4. The method as specified in claim 1, wherein said rapid quenching is to a temperature of less than about 1400° F. and said rapid quenching is conducted under nonreactive conditions. 
     
     
       5. The method as specified in claim 1, wherein prior to heating said filler metal is positioned proximate to and also above the adjacent portions of said tubing and said base member. 
     
     
       6. The method as specified in claim 1, wherein said filler metal consists essentially of 82 weight percent gold and 18 weight percent nickel. 
     
     
       7. The method as specified in claim 1, wherein said filler metal consists essentially of 70 weight percent gold, 22 weight percent nickel and 8 weight percent palladium. 
     
     
       8. The method as specified in claim 1, wherein said filler metal consists essentially of 50 weight percent gold, 25 weight percent nickel and 25 weight percent palladium. 
     
     
       9. The method as specified in claim 1, wherein said retained tubing and said base member and said filler metal are heated to a temperature of from about 1900° F. to about 2230° F. 
     
     
       10. The method as specified in claim 9, wherein said even heating within said temperature of from about 1900° F. to about 2230° F. does not exceed about 8 minutes to avoid excessive reaction between said filler metal and said parts being brazed. 
     
     
       11. The method of brazing corrosion resistant, nickel-based, thin-walled tubing having a wall thickness of less than about 12 mils and which includes substantial proportions of nickel, chromium and molybdenum with an iron content limited to a maximum of 7 percent by weight to a stainless steel base member without introducing stress corrosion cracks in the tubing and also avoiding carbon precipitation in the brazed corrosion resistant tubing, which method comprises: retaining said tubing and said base member to be brazed in adjacent positions desired for the brazed product and positioning a filler metal principally comprising gold as a major constituent and nickel as a minor constituent proximate the adjacent portion of said tubing and said base member;   evenly heating said tubing and said base member and said filler metal under vacuum conditions to a temperature of at least about 1900° F. for a sufficient period of time not exceeding about 8 minutes to avoid excessive reaction between said filler metal and said parts being brazed and to allow any carbide precipitate formed during heating to redissolve and to permit full uniform flow of said filler metal between said tubing and said base member; and rapidly quenching said retained and heated members in a gaseous atmosphere which is non-reactive with respect to said retained and heated members to a temperature of less than about 1400° F. to avoid carbide precipitation in said tubing.